Paper trimming machine and anti-backlash positional servo system therefor



July 6, 1965 'r. H. BROWN 3,193,

PAPER TRIMMING MACHINE AND ANTI-BAGKLASH v POSITIONAL SERVO SYSTEM THEREFOR Filed Jan. 17, 1961 3 Sheets-Sheet l 54 IN VEN TOR.

THOMAS H. BROWN July 6, 1965 'r. H. BROWN PAPER TRIMMING MACHINE AND ANTI-BACKLASH OSITIONAL SERVO SYSTEM THEREFOR S Sheets-Sheet 2 Filed Jan. 17. 1961 y 6, 1965 T- H. BROWN 3,193,745

PAPER TRIMMING MACHINE AND ANTI-BACKLASH POSITIONAL SERVO SYSTEM THEREFOR Filed Jan. 17. 1961 3 Sheets-Sheet 5 FIG. 4

P0 W51? JUPPL Y REL/546E j 6 HMPL/F/ER ll a4 l 9 FORWARD f i AMPL/F/ER 70 FAST/640W AMPL/F/ER o- JINVENTOR. THOMAS-J1! BROWN WTiRN Y5 United States Patent 3,193,745 PAPER TRIMMING MACHINE AND ANTI-BACK- LASH PUSITIONAL SERVO SYSTEM THEREFOR Thomas H. Brown, New Haven, Conn., assignor to The Smith and Winchester Manufacturing Company, South Windham, Conn., a corporation of Connecticut Filed Jan. 17, 1961, Ser. No. 83,339 6 Claims. (Cl. 318-29) The present invention relates to cutting and trimming machines for paper and the like and is more particularly concerned with a trimming machine having an adjustable back gauge for selectively positioning the stock to be cut.

It is a primary object of the present invention to provide an improved trimming machine for paper and the like which rapidly and accurately positions the stock in the desired cutting or trimming position.

It is a further object of this invention to provide an improved trimming machine having a back gauge for positioning the paper to be cut, which back gauge is quickly and accurately positioned by power means controlled from a remote position.

It is a still further object of this invention to provide a back gauge position control system whose accuracy is relatively unaffected by normal wear and tear on the mechanical components and which can be easily installed on most trimming machines so as to greatly increase the rate of accurate operation.

It is an additional object of this invention to provide a back gauge position control system for trimming machines and the like which is accurate and reliable in operation as well as being economical to manufacture and easy to opcrate.

It is a still further object of this invention to provide a back gauge position control system for paper trimming machines which is quickly and easily adapted to auto matic or semi-automatic operation without impairing the accuracy of the system.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claims.

In the drawings:

FIG. 1 is a perspective view of a trimming machine showing the movable back gauge;

FIG. 2 is a side elevation view of a portion of the back gauge drive and control system;

FIG. 3 is a block diagram of a preferred embodiment of the control system of this invention and schematically shows a portion of the trimming machine of FIG. 1; and

FIG. 4 is a schematic view of the bridge circuit portion of the control system of FIG. 1.

Turning now to the illustrated preferred embodiment of this invention and particularly FIGS. 1 and 2, it is noted that the trimming machine generally designated comprises a base 12 having upright side members 13 and a cross head member 15 disposed above a generally planar table 17. Table 17 extends in front of and to the rear of pedestals 13 so as to support stock that is to be trimmed and stock that has been trimmed to the desired size. A cutting blade 18 is mounted for vertical reciprocating movement along an axis generally perpendicular to table 17 and positioned to operate along a cutting line 19 (shown dotted in FIG. 1). The precise mode of operation of the cutting blade forms no part of this invention except that, for the purpose of facilitating description of this improved trimming machine, it is assumed that the line of operation of the knife is fixed relative to table 17. Stock 3,193,745 Patented July 6, 1965 placed on table 17 is positioned relative to the cutting line by a movable back gauge 20 that is slidably mounted on table 17 and guided for movement toward and away from cutting line 19 by rail or guide tube 22 disposed along one side of table 17. Controlled movement is imparted to back gauge20 by a lead screw 25 extending (see FIG. 2) adjacent and parallel to guide rail 22 and in threaded engagement with nut 26 which is secured to back gauge 20. Rotation of lead screw 25 by drive means generally designated 28 in FIG. 1 will effect the desired movement of back gauge 20 toward and away from the cutting line 19.

A back gauge drive mechanism 28 suitable for use with the trimming machine of this invention is more clearly illustrated in FIG. 2 wherein the lead screw 25 is provided with a drive pulley 30 that is driven by electric motor 32 through a speed reduction unit 34 whose output shaft 35 is provided with a pulley 36 that is connected to pulley 30 by drive belt 37. Motor 32 of the illustrated preferred embodiment is a reversible motor and unit 34 is provided with electromagnetic clutches generally designated 38 to produce rotation of output pulley 36 at two speeds in a forward direction and a single speed in a reverse direction as requested by the control unit hereinafter explained in greater detail.

More precisely, as hereinafter more fully explained, the mechanism 28 of the preferred embodiment is arranged to'provide lead screw rotation at fast and slow speeds in a direction to produce forward back gauge movement and at high speed only in a direction to produce reverse back gauge movement. In order to sense the rotational position of lead screw 25 relative to a preselected reference point and thus the physical position of back gauge 20 relative to the fixed cutting line 19, there is provided a helical potentiometer 40 whose movable arm or tap is connected to lead screw 25 through a speed reduction unit From the foregoing description of the basic drive structure of the trimming machine of FIG. 1, it is noted that back gauge 20 is driven in a cantilever fashion by the rotation of lead screw 25 that engages a fixed nut 26 carried by the back gauge. Such a drive arrangement permits the table to have a continuous surface thereby facilitating the handling of the paper stock that is carried thereon. The electric motor drive and speed control mechanism can, of course, be other than electricalin its motive power and, for the requirements of this invention, it is only necessary that it be capable of rotating the lead screw at two speeds (fast and slow) to effect movement of the back gauge toward the cutting line and at a single speed (high) to effect movement of the back gauge away from the cutting line. The position of the movable tap of potentiometer 40 is proportional to back gauge position and the change in resistance between the tap and one end of the resistance can be utilized to operate a position control system on a back gauge position indicator.

Automatic or semi-automatic control of the motor drive means and therefore of the position of back gauge 20 relative to the cutting line 19 in accord with one aspect of this invention is most clearly understood by reference to FIGS. 3 and 4 wherein it is seen that drive means 28 includes a contactor or switching chassis 49 through which power is supplied to the motor 32 and the speed control clutches. Three-phase power to reversible motor 32 is supplied either through a forward contactor or switching device 50 or a reverse direction contactor or switching device 51. Single-phase power is supplied through a conventional DC. power supply 53. and through either a fast contactor 54 or a slow contactor 55 to the proper clutch to achieve the desired speed. It is noted at this time that switching devices 50 and 51 and the control back gauge position.

3 switching devices 54- and 55 are interlocked in any desired manner to preclude simultaneous closure.

In order to control the energization of the various motor direction and speed clutch contactors, the helical potentiometer 4t and a resistance control unit designated operators control unit 53 are connected in a Wheatstone bridge arrangement whose input terminals 60 and 61 are energized from a 600 volt regulated power supply 62. The output terminals 64 and as are connected to what is designated a Sensor unit 66 that includes several amplifiers each of which is energized from a 300 volt regulated power supply 67 and whose various output terminals 68, 69, 7t) and 71 are connected through appropriate conductors to the energizing or control coils on the contactors. The precise arrangement of the bridge circuit is most easily understood from FIG. 4 wherein it is seen that the total resistance of helical potentiometer 49 forms two legs of the bridge arrangement with the movable tap 72 (that is connected to lead screw 2-5 for movement proportional thereto) forming one bridge output terminal 65. The remaining two legs of the Wheatstone bridge are generally comprised of a series of resistances 73, 74, 75 and 76, some or all of which can be made adjustable to calibrate the bridge circuit. In the preferred arrangement, resistances '73 and 74 have their taps 73a and 74a mechanically connected together for simultaneous movement and are selectively variable to The movable tap 77 of resistance '76 forms a vernier adjustment and is the other bridge output terminal 64. Once the various resistances of the illustrated embodiment have been adjusted so that the bridge balance position corresponds to the desired gauge position, it is apparent that movement of taps 73a and 74a will unbalance the bridge circuit and that movement of tap 70 on the helical potentiometer 40 in the appropriate direction will bring about a rebalancing of the bridge. It is noted at this point that the selective unbalancing of the bridge circuit to change back gauge position can also be effected by the provision of a series of resistances that are connectable in the bridge circuit through the closing of appropriate switches and that the closing of the switches can be effected by a stepping relay or similar device to completely automate step-by-step movement of the back gauge.

When utilizing the illustrated preferred circuit, the output terminal 65 is connected to the grid of the input stage of a first amplifying device designated reverse amplifier whose output terminal 68 is connected to the operating coil 86) of the reverse contactor 51 and to operating coil 81 of fast contactor 54. Output terminal 64 is connected to the grid of the first stage of a second amplifier designated the forward amplifier whose output terminal 6d is connected to the operating coil 82 of the forward contactor 50. Additionally, the inputs to the forward and reverse amplifiers are connected together through resistance 84- across which the bridge unbalance potential is developed. The center tap of resistance 84 and each of the amplifiers is connected to a common ground. When the bridge circuit is in balance, there will be no difference of potential between bridge output terminals 64 and 65' and, by utilizing direction control amplifiers arranged to produce no output signal when there is no potential difference between the inputs, no power is supplied to operating coils 80 and 82 of the respective contactors and no power will be supplied to operate the back gauge drive motor. When the bridge is unbalanced in the reverse direction, the output of the reverse amplifier is arranged to be substantially greater than the output of the forward amplifier and the reverse contactor and the fast contactor will close thereby to energize the motor in the reverse direction to move the back gauge away from the cutting line at fast speed. In a similar manner forward movement of the back gauge is achieved upon unbalance of the bridge circuit in the forward direction so as to close the forward contactor.

The aforedescribed direction control amplifiers can be of any conventional type but it has been found that vacuum tube amplifiers of the Class B type perform ade quately. These amplifiers are biased in accordance with the output polarities of the bridge circuit to operate as stated and in accordance with conventional techniques.

In accordance with the teachings of this invention, the output terminal 64 is also connected to a third amplifier of conventional Class B type designated the slow-fast or speed amplifier having two outputs 66 and 67, one of which is connected to the operating coil 36 of fast contactor 54 and the other to the operating coil 87 of slow contactor 55. Upon occurrence of a large magnitude of unbalance of the bridge circuit in the forward direction such that the input to the speed amplifier is large, the output of this amplifier will be of suflicient magnitude to close fast contactor 54 (thereby holding the slow contactor open) so as to energize the high speed clutch arrangement of the motor drive and move the back gauge at high speed toward the cutting line. As the back gauge approaches the desired position, the magnitude of the unbalance potential supplied to the speed amplifier will decrease so that fast contactor 54 will be deenergized and slow contactor 87 will be energized; thus the final forward movement of the back gauge is at slow speed.

As is apparent from the foregoing description, a single reverse speed is provided, which reverse speed is sufficiently great so that the inertia of the moving system including the motor drive unit (as Well as whatever inertia is provided by the back gauge itself) will be sufficient t0 cause overtravel of the back gauge beyond the balanc position thereby to create a small unbalance in the forward and speed control reverse direction which unbalance is sensed by amplifiers to close the forward contactor and the slow contactor and bring the back gauge forward into the balance position at a low speed wherein the inertia will not cause .overtravel. Such an arrangement insures that the normal wear on the drive mechanism as well as the normal manufacturing tolerances in the drive mechanism, the lead screw, helical potentiometer etc., will not materially affect the accuracy of the positioning of the back gauge since all back lash, etc. will be compensated for by requiring final balancing movement of the bridge and back gauge to be in the forward direction. Additionally, the calibration of the bridge balance point relative to gauge position can be adjusted to provide such further compensating adjustment as is necessary.

Turning now to a typical complete cycle of operation, it is noted that varying the position of tap 77 on potentiometer '76 to introduce an unbalance in the bridge circuit and thus produce a difference of potential between the output terminals 64 and 65, such that an unbalance signal is applied to the appropriate direction amplifier. For example, if the polarities of the system are such that unbalancing the bridge in the forward direction produces a positive potential at terminal 64- then this potential will be amplified to close the forward contactor and its magnitude will be sensed by the speed amplifier to close either the slow or the fast contactor in accordance with the magnitude of the unbalance. The motor and drive unit will then supply power to the lead screw to advance the back gauge in the desired direction. As the back gauge advances, the position of the movable tap '70 on potentiometer 40 changes so as to attempt to rebalance the bridge circuit. As the magnitude of potential difference between the output terminals decreases, the slow contactor will be energized and the back gauge will approach the balance position at low speed and stop with no overtravel in the desired position. If, however, the bridge circuit is unbalanced in the reverse direction, the reverse amplifier will conduct to energize the reverse contactor and drive the back gauge in a reverse direction at high speed. As the back gauge approaches the balance position determined by the position of the movable tap 70 connected for movement proportional to the lead screw, the speed remains a constant and the inertia of the moving system will cause the tap to move beyond the balance position and signal the forward amplifier to energize the forward contactor and the speed amplifier to energize the slow cont-actor to bring the tap on the helical potentiometer into the balance position and the back gauge into the desired position. Again, the final balance position is achieved by movement in the forward direction so as to eliminate the inherent back lash of the lead screw and nut as well as the inaccuracies of the motor drive system as factor to be considered in the accuracy of the positioning of the back gauge.

It is also noted that the simplicity of this system permits substantial economies in the automation of paper trimming machines without sacrificing the high accuracy which is required in this type of trimming operation. Additionally, the control system illustrated herein is easily adaptable to automatic operation as, for example, by the utilization of a plurality of predetermined resistance values that are selected in accordance with the desired back gauge position by a stepping relay. The simplicity and ease of operation of this control system makes its incorporation into existing trimming machines a relatively simple operation and eliminates special training of personnel to accomplish its effective operation.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.

I claim:

1. A trimming and cutting machine for paper and the like comprising a table, a cutting device operable along a cutting line on said table, a back gauge movable along said table toward and away from the cutting line, motor drive means connected to said back gauge and operable to move said back gauge at fast and slow speeds toward the cutting line and at fast speed only away from the cutting line, a normally balanced bridge circuit including a resistance having a movable tap, means connecting said movable tap to said back gauge for movement proportional therewith, control means to selectively unbalance said bridge circuit in a forward or reverse direction in accordance with the desired back gauge position, means connected to said bridge circuit for sensing the direction of bridge circuit unbalance effected by said control means, the output of said last named means being connected to said motor drive means to initiate movement of said back gauge and said tap in a direction to rebalance said bridge circuit at fast speed forward for large unbalance and at slow speed forward for low magnitude of bridge unbalance, the inertia of the moving system including said motor drive means and the back gauge being sufficient when moving away from the cutting line to overtravel the balance position of the bridge circuit thereby to require forward back gauge movement at low speed as the final rebalancing movement.

2. A trimming and cutting machine for paper and the like comprising a table, a cutting device operable along a cutting line on said table, a back gauge movable along said table toward and away from cutting line, motor drive means connected to said back gauge to move said back gauge toward and away from the cutting line, said motor drive means including a forward direction switching device and a reverse direction switching device interlocked therewith to preclude simultaneous closing thereof, a normally balanced bridge circuit including a resistance having a movable tap, means connecting said movable tap to said back gauge for movement proportional to back gauge movement, control means to selectively unbalance said bridge circuit in a forward or reverse direction in accordance with the desired back gauge position, a first amplifier connected to the bridge circuit output to amplify the magnitude of bridge circuit unbalance in a reverse direction, the output of said first amplifier being connected to said reverse switching device to control energization thereof, a second amplifier connected to the output of said bridge circuit to amplify the magnitude of bridge circuit unbalance in a forward direction, theoutput of said second amplifier being connected to said forward switching device, to control energization thereof, said first and second amplifiers having zero output when said bridge circuit is balanced whereby unbalancing of said bridge by said control means will cause one of said switching devices to close to effect movement of said back gauge and said tap in a direction to rebalance said bridge, the inertia of the moving system including said motor drive means and the back gauge being sufiicient when moving away from the cutting line to overtravel the balance position of the bridge circuit thereby 'to require forward back gauge movement as the final rebalancing movement.

3. The trimming and cutting machine asset forth in claim 2, wherein a third amplifier is connected to the output of said bridge circuit to provide an output signal proportional to the magnitude of bridge unbalance in the forward direction, said motor drive means is provided with a third switching means to effect fast or slow forward speed when the forward speed switching device is closed and wherein the output of said third amplifier is connected to said third switching means thereby to control the rate of forward movement of the back gauge in accordance with the magnitude of bridge circuit unbalance.

4. A back gauge positoning system for paper trimming machines of the type having a table, a cutting device operable along a cutting line on the table, and a back gauge mounted on said table for movement therealong, comprising motor drive means connected to the back gauge and operable to effect movement of the back guage toward and away from the cutting line, said motor drive means being arranged to selectively provide fast and slow speeds toward said cutting line and only fast speed away from said cutting line, a normally balanced bridge circuit having input and output terminals and including a resistance having a movable tap connected to said back gauge for movement proportional to back gauge movement, control means for selectively unbalancing said bridge circuit, amplifying means connected to the output terminals of said bridge circuit, said amplifying means being arranged to sense the direction and magnitude of bridge unbalance effected by said control means, the output of said amplifying means being connected to said motor drive means to initiate movement of the back gauge in a'direction of rebalance said bridge circuit, the inertia of the moving system including said motor drive means and the back gauge being suflicient when moving away from the cutting line to overtravel the balance position of said bridge circuit thereby to require forward back gauge movement as the final rebalancing movement.

5. A trimming and cutting machine for paper and the like comprising a table, a cutting device operable along a cutting line on said table, a back gauge positioned on said table for movement toward and away from the cutting line, a nut carried by said back gauge, a lead screw in engagement with said nut, motor drive means connected to said lead screw and operable to rotate said lead screw at fast and slow speeds when rotating in the direction to move said back gauge toward said cutting line and at fast speed only when rotating said lead screw in a direction to move said back gauge away from said cutting line, a normally balanced bridge circuit having input and output terminals and including a helical potentiometer having its movable tap connected to said lead screw for movement proportional thereto, a variable resistance for selectively unbalancing said bridge circuit, amplifying means connected to the output terminals on said bridge circuit, said amplifying means being arranged to sense the direction and magnitude of bridge unbalance effected by said variable resistance, the output of said amplifying means being connected to said motor drive means to initiate movement of the lead screw and back gauge in a direction to rebalance said bridge circuit, the inertia of the moving system including said motor drive means and said back gauge being sufiicient when moving away from the cutting line to overtravel the balance position of the bridge circuit so as to require forward back gauge movement as the final rebalancing movement.

6. The trimming and cutting machine as set forth in claim 5 wherein said motor drive means includes a for ward direction switching device operable to effect rotation of said lead screw to move said back gauge toward the cutting line, a reverse direction switching device operable to effect rotation of said lead screw away from the cutting line and a third switching device operable to effect fast or slow lead screw rotation when said forward switching device is energized, and wherein said amplifier means includes a first amplifier connected to the bridge circuit to amplify the magnitude of bridge unbalance in a reverse direction and having its output connected to control the operation of said reverse direction switching device, a second amplifier connected to the bridge circuit to amplify the magnitude of bridge unbalance in a forward direction and having its output connected to References Cited by the Examiner UNITED STATES PATENTS 2,520,495 8/50 Dehn 83-467 2,860,705 11/58 Thumim 214-1.6 2,889,507 6/59 Kennedy et al 31829 2,916,801 12/59 Lyttle 318162 2,971,142 2/61 Montross 318-29 3,061,764 10/62 St. Paul et a1 318162 3,028,531 4/62 Heiberger et al 31829 JOHN F. COUCH, Primary Examiner.

CARL W. TOMLIN, Examiner. 

1. A TRIMMING AND CUTTING MACHINE FOR PAPER AND THE LIKE COMPRISING A TABLE, A CUTTING DEVICE OPERABLE ALONG A CUTTING LINE ON SAID TABLE, A BACK GAUGE MOVABLE ALONG SAID TABLE TOWARD AND AWAY FROM THE CUTTING LINE, MOTOR DRIVE MEANS CONNECTED TO SAID BACK GAUGE AND OPERABLE TO MOVE SAID BACK GAUGE AT FAST AND SLOW SPEEDS TOWARD THE CUTTING LINE AND AND AT FAST SPEED ONLY AWAY FROM THE CUTTING LINE, A NORMALLY BALANCED BRIDGE CIRCUIT INCLUDING A RESISTANCE HAVING A MOVABLE TAP, MEANS CONNECTING SAID MOVABLE TAP TO SAID BACK GAUGE FOR MOVEMENT PROPORTIONAL THEREWITH, CONTROL MEANS TO SELECTIVELY UNBALANCE SAID BRIDGE CIRCUIT IN A FORWRAD OR REVERSE DIRECTION IN ACCORDANCE WITH THE DESIRED BACK GAUGE POSITION,MEANS CONNECTED TO SAID BRIDGE CIRCUIT FOR SENSING THE DIRECTION OF BRIDGE CIRCUIT UNBALANCE EFFECTED BY SAID CONTROL MEANS THE OUTPUT OF SAOD LAST NAMED MEANS BEING CONNECTED TO SAID MOTOR DRIVE MEANS TO INITIATE MOVEMENT OF SAID BACK GAUGE AND SAID TAP IN A DIRECTION TO REBALANCE SAID BRIDGE CIRCUIT AT FAST SPEED FORWARD FOR LARGE UNBALANCE AND AT SLOW SPEED FORWARD FOR LOW MAGNITUDE OF BRIDGE UNBALANCE, THE INERTIA OF THE MOVING SYSTEM INCLUDING SAID MOTOR DRIVE MEANS AND THE BACK GAUGE BEING SUFFICIENT WHEN MOVING AWAY FROM THE CUTTING LINE TO OVERTRAVEL THE BALANCE POSITION OF THE BRIDGE CIRCUIT THEREBY TO REQUIRE WARD BACK GAUGE MOVEMENT AT LOW SPEED AS THE FINAL REBALANCING MOVEMENT. 